The present invention relates to a lithographic web-fed rotary printing press for printing high quality images on a running paper web. In particular, the present invention relates to a web-fed rotary printing press which can be operated in a perfecting mode for printing multi-color images on both sides of a single web or which can alternatively be run in a non-perfecting mode for printing a multi-color image on a first web and if desired a second multi-color image on a second side of a second web.
Printers of high quality images, e.g. magazines, brochures and advertisements, etc., tend to employ more and more compact printing presses, while at the same time it is desired to further increase the productivity or speed of the presses and the quality of the printed products. Moreover, there is the further desire to achieve a more flexible press design which, particularly in the market of short run color printing (SRCP), allows for a larger number of different kinds of print jobs to be run on the same printing press, accommodating the growing variety of printed products and the reduction of the average number of products printed in each print job.
In practice, however, it is often required to run a first print job in a perfecting mode, in which both sides of a running paper web are printed with different multi-color images at the same time, and afterwards run a high speed print job in a non-perfecting mode, in which only one side of a paper web is printed with a multi-color image.
U.S. Pat. No. 5,136,942 purports to disclose a printing press for printing banknotes, in which a web is passed around a first impression cylinder to be printed on a first side with a first multi-color image and is afterwards passed around a second impression cylinder adjacent to the first impression cylinder, to be printed with a second multi-color image on the second side. The described banknote press does not permit the printing of two multi-color images on two different webs running through the printing press at the same time.
European Patent Publication No. 0 132 858 describes a printing press with a blanket to blanket printing unit for printing banknotes. The printing unit has first and second separable blanket cylinders, each of which is in contact with four plate cylinders for consecutively applying four images of different colors directly onto each blanket cylinder, thereby providing complete first and second multi-color images on each blanket cylinder. Afterward, when the cylinders are brought into contact with each other, the multi-color images provided on the first and second blanket cylinders are transferred to the web running between the blanket cylinders. In order to provide for a free passage of the web, e.g. when the printing unit is not in operation and no transfer of images to the web is desired, the first and second blanket cylinders are separated from each other. This printing press does not permit simultaneous processing of two webs in a non-perfecting mode.
It is an object of the present invention to provide a high speed web-fed rotary printing press which can be operated in either a perfecting mode or a non-perfecting mode, to print either high quality images on both sides of a single web or single images on a first side of a first web and, if desired, on a second side of a second web.
It is a further object of the present invention to provide a highly flexible printing press which may be adapted to different print jobs which are consecutively run on the printing press.
The present invention is directed to a printing unit for a web-fed rotary printing press for alternatively printing only a first web in a perfecting mode and for printing the first web and a second web in a non-perfecting mode, wherein the first and second webs travel through the printing unit from an upstream end to a downstream end thereof. The printing unit comprises a first impression cylinder having a plurality of first blanket cylinders and a corresponding plurality of first plate cylinders arranged around at least a portion of a periphery thereof and a second impression cylinder located adjacent to the first impression cylinder and having a plurality of second blanket cylinders and a corresponding plurality of second plate cylinders arranged around at least a portion of a periphery thereof. In the perfecting mode, the first web is passed over the first impression cylinder to be printed on a first side thereof and is then passed through a gap between the first and second impression cylinders to the second impression cylinder to be printed on a second side thereof, and, in the non-perfecting mode, the first web is passed over the first impression cylinder and the second web is passed over the second impression cylinder.
According to a further embodiment of the invention, any of the first and/or second plate cylinders and its respective first and/or second blanket cylinder may comprise a direct imaging unit while the remaining plate cylinder/blanket cylinder units may comprise offset printing units.
According to a further object of the present invention, first and second infeed rollers are arranged upstream of the first and second impression cylinders, in order to feed the incoming first and second webs substantially tangentially to the first and second impression cylinders, respectively, and to the corresponding one of the first and second blanket cylinders.
According to a further exemplary embodiment of the present invention, first and second exit rollers are provided downstream of the first and second impression cylinders, in order to pass the respective webs substantially tangentially away from the respective one of the first and second impression cylinders and the respective one of the first and second blanket cylinders.
According to a further exemplary embodiment of the invention, dryers are provided for drying, in the perfecting mode, the first and/or second sides of the single web and, in the non-perfecting mode, for drying the first and second webs.
The present invention eliminates elongation or fan out of the web which is usually caused by dampening liquids in prior art printing presses having printing units for applying different colors separated from each other. Therefore, printing quality is improved.
The present invention also allows a make-ready operation to be performed on the blanket and/or plate cylinders associated with one of the first and second impression cylinders, while, at the same time, the other one of the first and second impression cylinders can be used for printing the web in a non-perfecting mode.
Moreover, the time required for make-ready operations can be further reduced if the printing press is equipped with inking units for applying known single fluid inks to the printing plates of the respective plate cylinders associated with each impression cylinder.